I can definitely see how it would get frustrating to have to go through Wi-Fi diagnostics ever five minutes. I found an article with steps you can take when you have network issues like this.
I recommend following the solutions under the sections titled "Symptom: The network connection drops unexpectedly" and "Symptom: After restarting or waking from sleep, my computer might not connect to the Internet" in the following article:
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All the best,
I am having this exact issue with my iMac 21,5", totally ruins streaming and gaming. It's not as frequent as every 5 minutes but it is persistent. I can get back the internet access by turning wifi on and off, or by launching Network Diagnostics in which case it usually fixes itself after a couple of seconds, and sometimes I have to go through the steps described by Rocsta13.
I've tried the solutions linked to by Sheila M. but to no avail. I've also tried creating a new location, and adding new DNS servers. I am on a wifi network which other people use as well but I seem to be the only one with this problem. Could it be a ISP or router problem or something to do with my mac?